Conventionally, a pretensioner mechanism for retracting a webbing is mounted in a seatbelt retractor provided for a seat of a vehicle for the purpose of holding a passenger effectively and securing safety of the passenger in case of emergency such as vehicle collision.
For instance, a take-up drum onto which a webbing is wound has flange portions formed so as to overhang radially at the both ends of a shaft central direction. A webbing is wound around a drum main body portion between the both flange portions. Further, a coupling body made of a steal material or the like is press-fitted and fixed in a coupling hole portion formed in one of the flange portions in a manner that relative rotation thereof with respect to the take-up drum is disabled (for instance, refer to paragraphs 0010 to 0059 and FIG. 1 through FIG. 9 of Japanese Laid-open Patent Publication No. 2003-335217).
In case of vehicle collision, the pretensioner mechanism operates in the following manner so as to retract the webbing onto the take-up drum and hold a passenger. First, gas is generated from a gas generating member and a rack is caused to move, whereby a pinion gear body is rotated and driven. A cam surface is formed on an inner peripheral surface of one side portion of the pinion gear body and a plurality of clutch rollers are arranged between this cam surface and the coupling body. Then, the rotation of the pinion gear body guides the respective clutch rollers to the cam surface so as to be depressed and operated radially inwardly.
The respective clutch rollers depressed and operated are brought in an engaged state between the cam surface of the pinion gear body and the outer peripheral surface of the engagement shaft portion of the coupling body, whereby the pinion gear body and the coupling body are caused to rotate integrally. Accordingly, the take-up drum is rotated and driven in a webbing-pull-out direction and thereby the webbing is retracted.